The vastly increased data rates that can be handled in the optical spectrum is channelling creativity to address heretofore unsolved problems. Commercially available single mode fibers of an acceptable attenuation and dispersion are making full scale data systems a reality. While a single mode fiber transmitting at a single wavelength can handle a considerable amount of data, wavelength multiplexing of data through this fiber provides an even more vast data transmission capability. Unfortunately, the state-of-the-art has failed to produce a wavelength demultiplexing scheme which is consistent in the level of preciseness and reliability needed for acceptable operation.
The known methods for accomplishing wavelength demultiplexing generally employ discrete dispersive and focusing elements in the form of aligned gratings or prisms or have multilayer interference filters in combination with focusing elements. These are limited in the accuracy of their fabrication and assembly, their stability, the reliability of the packaging, by the mechanical holders or cements that hold them together, the number of channels which are capable of being demultiplexed and, of course, the overall cost of such an arrangement.
There has been no incorporation of the optical demultiplexing function into the technology that advantageously can accommodate high data rates, that being the VLSI or VHSIC technologies. Interface problems associated with coupling separated demultiplexers to integrated circuit chips introduce a great number of comprimises that limit the full utilization of the chip's capabilities which could otherwise meet the high data rate transmission capabilities of optical transmission systems. An example of such an optical multiplexing-demultiplexing system, which in itself is a noteworthy advance in the state-of-the-art, is referred to in the paper by C. R. Chubb et al entitled "Development of the Multiwavelength Monolithic Integrated Fiber Optics Terminal, SPIE, Vol. 317 Integrated Optics and Milimeter and Microwave Integrated Circuits (1981).
Thus, there is a continuing need in the state-of-the-art for wavelength division demultiplexer capable of being fabricated in accordance with established integrated circuit fabrication techniques to provide up to fifty discrete wavelength demultiplexed channels.